Tag Archives: sperm quality

New research by scientists at the University of Nottingham suggests that environmental contaminants found in the home and diet have the same adverse effects on male fertility in both humans and in domestic dogs.

There has been increasing concern over declining human male fertility in recent decades with studies showing a 50% global reduction in sperm quality in the past 80 years. A previous studyby the Nottingham experts showed that sperm quality in domestic dogs has also sharply declined, raising the question of whether modern day chemicals in the home environment could be at least partly to blame.

In a new paper published in Scientific Reports, the Nottingham team set out to test the effects of two specific man-made chemicals namely the common plasticizer DEHP, widely abundant in the home (e.g. carpets, flooring, upholstery, clothes, wires, toys) and the persistent industrial chemical polychlorinated biphenyl 153, which although banned globally, remains widely detectable in the environment including food.

The researchers carried out identical experiments in both species using samples of sperm from donor men and stud dogs living in the same region of the UK. The results show that the chemicals, at concentrations relevant to environmental exposure, have the same damaging effect on sperm from both man and dog.

Leading the work, Associate Professor and Reader in Reproductive Biology at the School of Veterinary Medicine and Science, Richard Lea, said: “This new study supports our theory that the domestic dog is indeed a ‘sentinel’ or mirror for human male reproductive decline and our findings suggest that man-made chemicals that have been widely used in the home and working environment may be responsible for the fall in sperm quality reported in both man and dog that share the same environment.”

“Our previous study in dogs showed that the chemical pollutants found in the sperm of adult dogs, and in some pet foods, had a detrimental effect on sperm function at the concentrations previously found in the male reproductive tract. This new study is the first to test the effect of two known environmental contaminants, DEHP and PCB153, on both dog and human sperm in vitro, in the same concentrations as found in vivo.

Rebecca Sumner, who carried out the experimental work as part of her PhD, said “In both cases and in both subjects, the effect was reduced sperm motility and increased fragmentation of DNA.

Dr Sumner added: “We know that when human sperm motility is poor, DNA fragmentation is increased and that human male infertility is linked to increased levels of DNA damage in sperm. We now believe this is the same in pet dogs because they live in the same domestic environment and are exposed to the same household contaminants. This means that dogs may be an effective model for future research into the effects of pollutants on declining fertility, particularly because external influences such as diet are more easily controlled than in humans.”

Professor Gary England, Dean of the School of Veterinary Medicine and Science and Professor of Comparative Veterinary Reproduction said:“Since environmental pollutants largely reflect a Western way of life such as the effects of industry, the chemicals present in the environment are likely to depend on the location. An important area of future study is to determine how the region in which we live may affect sperm quality in both man and dog.”

The full research paper, ‘Independent and combined effects of diethylhexyl phthalate and polychlorinated biphenyl 153 on sperm quality in the human and dog’ is available here.

A study led by researchers at The University of Nottingham has discovered that the fertility of dogs may have suffered a sharp decline over the past three decades.

The research, published in the academic journal Scientific Reports, found that sperm quality in a population of stud dogs studied over a 26-year period had fallen significantly.

The work has highlighted a potential link to environmental contaminants, after they were able to demonstrate that chemicals found in the sperm and testes of adult dogs – and in some commercially available pet foods – had a detrimental effect on sperm function at the concentrations detected.

As ‘man’s best friend’ and closest companion animal, the researchers believe that the latest results may offer a new piece of the puzzle over the reported significant decline in human semen quality – a controversial subject which scientists continue to debate.

Dr Richard Lea, Reader in Reproductive Biology in the University’s School of Veterinary Medicine and Science, who led the research said: “This is the first time that such a decline in male fertility has been reported in the dog and we believe this is due to environmental contaminants, some of which we have detected in dog food and in the sperm and testes of the animals themselves.

“While further research is needed to conclusively demonstrate a link, the dog may indeed be a sentinel for humans – it shares the same environment, exhibits the same range of diseases, many with the same frequency and responds in a similar way to therapies.”

The study centred on samples taken from stud dogs at an assistance dogs breeding centre over the course of 26 years. Professor Gary England, Foundation Dean of the School of Veterinary Medicine and Science and Professor of Comparative Veterinary Reproduction, who oversaw the collection of semen said: “The strength of the study is that all samples were processed and analysed by the same laboratory using the same protocols during that time and consequently the data generated is robust.”

The work centred on five specific breeds of dogs – Labrador retriever, golden retriever, curly coat retriever, border collie and German shepherd – with between 42 and 97 dogs studied every year.

Semen was collected from the dogs and analysed to assess the percentage of sperm that showed a normal forward progressive pattern of motility and that appeared normal under a microscope (morphology).

Over the 26 years of the study, they found a striking decrease in the percentage of normal motile sperm. Between 1988 and 1998, sperm motility declined by 2.5 per cent per year and following a short period when stud dogs of compromised fertility were retired from the study, sperm motility from 2002 to 2014 continued to decline at a rate of 1.2% per year.

In addition, the team discovered that the male pups generated from the stud dogs with declining semen quality, had an increased incidence of cryptorchidism, a condition in which the testes of pups fail to correctly descend into the scrotum.

Sperm collected from the same breeding population of dogs, and testes recovered from dogs undergoing routine castration, were found to contain environmental contaminants at concentrations able to disrupt sperm motility and viability when tested.

The same chemicals that disrupted sperm quality, were also discovered in a range of commercially available dog foods – including brands specifically marketed for puppies.

Dr Lea added: “We looked at other factors which may also play a part, for example, some genetic conditions do have an impact on fertility. However, we discounted that because 26 years is simply too rapid a decline to be associated with a genetic problem.”

Over the past 70 years, studies have suggested a significant decline in human semen quality and a cluster of issues called ‘testicular dysgenesis syndrome’ that impact on male fertility which also include increased incidence of testicular cancer, the birth defect hypospadias and undescended testes.

However, declining human semen quality remains a controversial issue – many have criticised the variability of the data of the studies on the basis of changes in laboratory methods, training of laboratory personnel and improved quality control over the years.

Dr Lea added: “The Nottingham study presents a unique set of reliable data from a controlled population which is free from these factors. This raises the tantalising prospect that the decline in canine semen quality has an environmental cause and begs the question whether a similar effect could also be observed in human male fertility.”